The present invention relates to a wire bonding method for improving the reliability of the fine wire bonding joint, a wire bonding apparatus, and a semiconductor device formed by using the wire bonding method and apparatus.
Heretofore, in the assembling process of semiconductor devices, there has been extensively used a method of using both thermal pressure bonding and supersonic wave vibration as a method of bonding a metal wire to the bonding pad on a semiconductor device. To meet the trend of reduction in size and pitch of the bonding pad in recent years, establishment of the wire bonding method for obtaining the bonding in higher reliability is necessitated. FIG. 24 shows a relationship between the load and application timing of supersonic wave vibration and the bonding time by the wire bonding method shown for example in Japanese Unexamined Patent Publication No. 279040/1992. According to the embodiment, there is adopted a multi-stage loading by employing a low load A between the high load and the low load B, so as to make the low load A lighter than the low load B. The application of the supersonic wave vibration is commenced at the time of the high load.
As described above, according to the conventional wire bonding method, the bonding load amount for duration from the contact of the metal wire with the bonding pad to the time of application of the supersonic wave vibration is constant. For this reason, there have been problems that, when the load amount at such time is set to a high amount to such a degree that nucleus of bond is formed, the deformation of metal wire becomes excessively large, while on the other hand, when the deformation amount is set to a low level to such a degree that the deformation amount can be suppressed, the nucleus of bond cannot be sufficiently formed. Furthermore, since the supersonic wave vibration is additionally applied during the application of load, the tendency for deformation of the metal wire to become excessively large is further accelerated, so that there has been a problem that formation of a fine wire bonding joint becomes impossible.
The present invention has been developed to solve the problems as described above, and an object of the present invention is to provide a wire bonding method and apparatus in which the nucleus of bond is sufficiently formed at the joint between the metal wire and bonding pad, and deformation amount of the metal wire can be set to a moderate level, so that the reliability of fine wire bonding joint is improved, and to obtain a high quality semiconductor device having highly reliable bond by using the above method and apparatus.